 |
|
 |
| ||
|
Hydrology 101
The dictionary defines hydrology as the science dealing with the occurrence, circulation, distribution, and properties of water on earth and its atmosphere. Humanity can't do much about how much rain falls from the clouds each year, but people have certainly tinkered endlessly with how and where water goes once it hits the ground. More tinkering with hydrology -- and what experts call the "hydrograph" (the level and rate of flow of a body of water over time) -- is promised in CALFED's three alternatives for fixing the Delta.
"They all involve new storage, so the main difference is in conveyance -- in the way water moves through the Delta," says the Contra Costa Water District's David Briggs.
While water historically flowed straight down from Sierra snowmelt into streams and rivers and through the Delta and Bay to the ocean, it has long been impeded by big dams, stored for later release in large reservoirs, and pumped out of waterways for export to cities and farms near and far. CALFED's Alternative 1 would do little to change the Delta's water movement system as it exists today. Alternative 2 enlarges the Old River channel feeding the state and federal water project pumps -- decreasing the high flow velocities toward the pumps that have long plagued fish and reducing big variations in water levels that often leave local farmers with high and dry irrigation intakes.
Alternative 2 also creates a brand new mini-canal between the town of Hood on the Sacramento River and the Mokelumne River. "It lifts a lot of fresh water from the Sacramento by brute force and dumps it into the Mokelumne," says Briggs. The main impact is more on water quality than hydrology. The canal will "freshen up" the Central Delta water supply, which is compromised by salt water intrusion. In times of drought and low Delta outflow, however, it may also help reduce reverse flows, when so much water is being sucked out by the big export pumps that the San Joaquin River near Antioch actually changes direction and flows east.
Neither Alternative 1 or 2 significantly changes how and where water is removed from the system for export - 100% is still being taken from the South Delta at the big pumps.
Alternative 3, however, removes the majority of the water much farther upstream by creating a new conveyance canal between Hood in the North and the pumps in the South, thereby circumventing the Delta. "The amount of water leaving the Delta is more or less the same but you're removing it from a different place," explains Briggs. The canal gives exporters the much desired flexibility to pump from two different locations (and thus avoid crunching endangered fish) and to get higher quality water at the upstream location. It may also minimize reverse flows by shifting some pumping upstream.
"If we go around the Delta with a channel, then we'll establish more historical flow patterns," says CALFED's Mark Cowin. "The net result is water moving toward the ocean from both the Sacramento and San Joaquin Rivers more often, as opposed to backing up on the San Joaquin side."
Clearly, none of the three alternatives bring the system back to nature, in terms of the historic hydrograph. All continue to alter the natural pattern, timing and amount of Delta outflow. The only return to nature in the hydrologic picture has nothing to do with channel modifications and canal construction but with increased flows released for environmental benefit, especially during drier periods when flows are more critical for fish. Both CALFED and Central Valley Water Project improvement programs call for such releases.
"The operational policies that go along with the physical changes make most of the hydrological difference," says Cowin.
The biggest effect on the shape of the Delta hydrograph could be caused by new storage. But even if CALFED built the maximum amount of storage under consideration (about 6 million acre feet), the changes to the hydrograph would be relatively minor in most years, says Cowin.
Whether it's managing flows or building new canals and reservoirs, it's clear that people will be further tinkering with an already tinkered-to-death water system (much of the tinkering has admittedly been for environmental restoration). On the technical side, debate continues to rage over what benefits may be derived from changing how water moves through the Delta. "Not everyone agrees on how this will all work, a lot relies on competing models and interpretation of data," says Briggs.
While the experts debate data, the public must make its own choices. Much of the popular hue and cry seems to be centered on the prospect of a peripheral canal reborn, and on associated echoes of the era of big water development. "Many people think a small peripheral canal will somehow increase the physical export capacity of the water projects, and thus create higher exports, " says Cowin. "But the pumps will still have a 15,000 cubic feet per second limit. This is the biggest, hydrology-related misunderstanding about CALFED."
Contact: David Briggs (510)688-8073 or Mark Cowin (916)653-2986
[ ABAG HOME | SFEP HOME ]
Copyright © 2002, San Francisco Estuary Project